Recently, radiation detectors such as Flat Panel Detectors (FPDs) are being implemented, in which a radiation sensitive layer is disposed on a Thin Film Transistor (TFT) active matrix substrate, and with which radiation can be converted directly into digital data. Radiographic image capturing devices, such as electronic cassettes, that employ such radiation detectors and capture radiographic images expressing irradiated radiation are also being implemented. Methods used by radiation detectors to convert radiation into electrical signals include an indirect conversion method, in which radiation is first converted into light with a scintillator and then the converted light is converted into charges with a photodiode, and a direct conversion method in which radiation is directly converted into charges with a semiconductor layer including amorphous selenium and the like. There are various materials that can be used in the semiconductor layer for each method.
When employing a radiation detector to capture radiographic images, excellent image quality needs to be secured while minimizing the dose of radiation with which a subject is irradiated. In order to acquire radiographic images with excellent image quality, exposure control conditions need to be set for a radiation source such that exposure is with an appropriate dose of radiation according to the imaging target site. A radiographic image capture system provided with an Automatic Exposure Control (AEC) function is therefore proposed in which a radiation detector detects a cumulative radiation dose of radiation irradiated through the subject, and an irradiation stop timing of radiation from the radiation source is controlled based on the detection result. It is proposed that pixels that detect the dose of irradiated radiation are embedded in the radiation detector, separately to pixels that capture radiographic images in order to implement the Automatic Exposure Control (AEC).
For example, Japanese Patent Application Laid-Open (JP-A) No. 2012-15913 describes a radiographic image capturing device in which plural pixels, including pixels for radiographic image capture and pixels for radiation detection, are disposed in a matrix shape in a detection region for detecting radiation, and the irradiated dose of radiation is detected by detecting charges flowing in signal lines connected to the pixels for radiation detection.